6.24的所有正約數(shù)之和為（　　�。�
A.36                                                         B.59

C.60                                                         D.58

7.若（a, b, c）=1，則下列式子一定成立的是（　　�。�

A.（a, b）=1                                             B.(a, b)=(b, c)

C.(a, c)=1                                                 D.((a, b) , c)=1

8.下列同余式組無(wú)公根的是（　　�。�
A.                                         B.

C.                                         D.

9.自然數(shù)6，12，18，28中是完全數(shù)的是（　　�。�
A.6與12                                                  B.6與18

C.12與28                                                 D.6與28

10.312的不同質(zhì)因數(shù)共有_______個(gè)。（　　　）
A.2                                                           B.3

C.4                                                           D.5